FAIR VALUE MEASUREMENTS (Level 3 Reconciliation) (Details) - Level 3 - Price Risk Management Instruments - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning asset balance	$ 109	$ 34	$ 95	$ 42
Net realized and unrealized gains:
Included in regulatory assets and liabilities or balancing accounts	(75)	(10)	(61)	(18)
Ending asset balance	$ 34	$ 24	$ 34	$ 24